Misfires of an internal combustion engine result in an increase in pollutants emitted during operation of the engine and may also result in damage to the catalytic converter in the exhaust system of the internal combustion engine. To meet statutory requirements for monitoring functions relevant to the exhaust gas, it is necessary to detect misfires in the entire rotational speed range and load range. In this context, it is possible that during operation with misfires, characteristic changes occur in the rotational speed characteristic of the internal combustion engine in comparison with normal operation without misfires. By comparing these rotational speed characteristics, it is possible to differentiate between normal operation without misfires and operation with misfires.
Therefore, a crankshaft angle range, which is referred to as a segment, may be assigned to a certain range of the piston movement of each cylinder. These segments may be implemented, for example, by marks on a sensor wheel, which is coupled to the crankshaft. The segment time during which the crankshaft passes over this angle range depends on the energy converted in the combustion cycle, among other things. Misfires result in an increase in segment times detected in synchronization with firing. Differences in segment times thus constitute a measure for the unsteady running of an internal combustion engine.
The marks on the sensor wheel are subject to mechanical tolerances, referred to below as tooth defects, with respect to their defined position, so that measured segment times may be falsified. These tooth defects may be ascertained and corrected through suitable algorithms as part of a tooth defect adaption. For this tooth defect adaption, the internal combustion engine is operated in a defined engine condition, which is associated with a great effort and cannot be implemented during normal operation of the internal combustion engine in particular. Therefore, there may be long periods of time without a tooth time adaption and thus without a tooth defect correction, during which certain segment times may be falsified.
The object now confronting those skilled in the art is to provide a possibility for determining segment times of a sensor wheel of an internal combustion engine by a simple method and thereby compensate for mechanical tolerances in the marks on the sensor wheel.